2.2 Protobalanus section
Five species in Protobalanus section were included in this study (Table 2). This section has species only exist in New World. Average pollen size of species in Protobalanus section (Lengths of equatorial axis average 23.17 μm and of polar axis average 27.01 μm) is the smallest in both length of equatorial axis and polar axis in the three sections. The variation of sizes, both length and width in equatorial view, of species in this section is the smallest in three sections. P/E ratio of pollen is the highest in three section. Pollen shapes tend to be spheroidal. Surface ornamentation of Protobalanus pollen is uniform (dense scabrate). Quercus cedrosensis and Quercus chrysolepisdisplay higher P/E ratio than that of other species.